A power supply system has been used which is configured to be able to supply power to load equipment using a rechargeable secondary battery and charge the secondary battery even during operation of the load equipment as necessary. Typically, such power supply systems are mounted on hybrid vehicles, electric vehicles, or the like including electric motors driven by secondary batteries as driving power sources. For example, in an electric vehicle, the vehicle is driven by driving a motor using power stored in the secondary battery. On the other hand, in a hybrid vehicle, the vehicle is driven by driving a motor using electric power stored in the secondary battery, or the vehicle is driven by driving the motor with the assistance of an engine. In a fuel cell vehicle, the vehicle is driven by driving a motor using electric power from a fuel cell, or the vehicle is driven by driving the motor using electric power stored in a secondary battery in addition to the electric power from the fuel cell.
In particular, in a hybrid vehicle formed to drive a generator using an internal combustion engine mounted on the vehicle to generate power, with which a secondary battery can be charged, SOC (State Of Charge) needs to be controlled to be at about midpoint (50-60%) between a fully charged state (100%) and a non-charged state (0%) so that the secondary battery can receive regenerative power and supply power to the motor immediately upon request.
Furthermore, when a secondary battery is overcharged or overdischarged, the battery performance is degraded and the lifetime is shortened, and therefore, charge/discharge has to be controlled by grasping SOC of the secondary battery. In general, charge/discharge control is performed in such a manner that excessive charge/discharge is restricted by properly setting inputtable/outputtable power (Win, Wout), which indicates the upper limit values of charging power and discharging power of a secondary battery, according to a battery state.
In addition, as a manner of secondary battery charge/discharge restriction, Japanese Patent Laying-Open No. 2005-137091 (referred to as Patent Document 1 hereinafter) discloses a control configuration in which charging electricity by regenerative braking is restricted according to a battery state during regenerative braking so as to prolong the lifetime of a secondary battery mounted on a vehicle. Specifically, during regenerative braking of the vehicle, the degree of deterioration of the secondary battery due to charge during regenerative braking is predicted, and in addition, the charging electricity during regenerative braking is restricted based on the predicted degree of deterioration.
Furthermore, W. B. Gu and C. Y. Wang, “THERMAL-ELECTROCHEMICAL COUPLED MODELING OF A LITHIUM-ION CELL,” ECS Proceedings Vol. 99-25 (1), pp 743-762 (referred to as Non Patent Document 1) proposes modeling for estimating a battery state using a battery model of capable of estimating the battery internal electrochemical reaction, for example, in a lithium-ion battery, as a technique of performing charge/discharge control by accurately estimating the remaining capacity (SOC) based on a secondary battery internal state.